Photoluminescence Properties of Silver(I) Complexes: From Extremely Long-Lived Phosphorescence to Ultrashort-Lived TADF

We review Ag(I) complexes with organic ligands that show ambient-temperature phosphorescence or thermally activated delayed fluorescence (TADF). Criteria for the assignment of the emission character are given. Two materials are highlighted: [Ag(dmp)(DPEPhos)]PF6 A (dmp: 2,9-dimethyl-1,10-phenanthroline, DPEPhos: bis[(2-diphenylphosphino)phenyl]ether), featuring an exceptionally long decay time of τ(phos) = 110 ms at ΦPL(phos) ≈50%, shows phenanthroline ligand-centered 3LC → S0 phosphorescence. The resulting large ΔE(S1–T1) gap (640 meV) inhibits the efficient thermal population of the S1 state. In contrast, the rationally modified Ag(dbp)(P2-nCB) B (dbp: 2,9-dibutyl-1,10-phenanthroline, P2-nCB: strongly electron-donating diphosphine ligand comprising a negatively charged nido-carborane cage) features low-lying states of (ligand + metal)-to-ligand charge transfer (1,3(L + M)L’CT) character. This reduces ΔE(S1–T1) to 80 meV, enabling fast and bright ambient-temperature TADF (radiative decay time: 1.4 μs at ΦPL(TADF) = 100%) with the decay time of more than 5 orders of magnitude shorter than that of A. The radiative properties of both compounds are outstanding compared to other pseudotetrahedrally coordinated metal complexes. In a second part, we extend the reviewed work by investigating both compounds by detailed DFT and TD-DFT calculations, including spin–orbit coupling. The results reflect the experimental trends. A is a potential highly sensitive oxygen sensor, while B might represent a new type of efficient OLED emitter material.